A study of the performance and chemical characteristics of composite reverse osmosis membranes prepared by plasma polymerization of allylamine

A study has been carried out of the performance and chemical characteristics of composite reverse osmosis membranes prepared by plasma polymerization of allylamine in a radio-frequency electric discharge. It has been shown that membranes can be prepared which simultaneously exhibit a high rejection for sodium chloride and a high water flux. The primary factors influencing the quality of the membranes are the choice of substrate material, the deposition time, and the power supplied to the discharge. Variations in rejection and flux as a function of applied pressure indicate that water flows through the membrane by both diffusive and bulk flow. A reduction in rejection and an increase in flux are observed when membranes are operated for prolonged periods or at higher temperatures (up to 60°C). Elemental analysis of plasma-polymerized allylamine shows that it can be represented by the stoichiometry C₃H_3.8N_0.9O_0.1. Infrared spectra show evidence for N? H, C?N, C?N, and C? H bond vibrations. ESCA spectra of the polymer surface show that the surface contains substantial amounts of both nitrogen and oxygen and that the nitrogen is present as either a nitrile or an imine group but not as an amine group. ESCA spectra of membranes used for reverse osmosis show that the surface loses nitrogen and gains oxygen with time and that this phenomenon is accelerated at higher operating temperatures. A decrease in rejection and an increase in flux accompanies these changes. It is postulated that most of the nitrogen in the polymer is present in the form of RR′C?NH or RR′C?NR″ type structures. The loss of nitrogen and gain in oxygen observed in the ESCA spectra of membranes run at elevated temperatures is explained by the hydrolysis of the proposed structures.     

Reverse osmosis by composite charged membranes

The charged membranes were prepared from the sulfonation and amination of SBR resins, and their reverse osmosis performances were investigated. The sulfonated membranes show high salt rejection. This result is in accord with the result of membrane potentials. Relatively excellent membranes were obtained by amination of the sulfonated membranes. This is probably owing to the formation of a dense charged region near the membrane surface; the composite charged membranes of sandwich-type are obtained by this method. The reverse osmosis performances of these membranes from various materials were made clear.     

Composite reverse osmosis membranes prepared by plasma polymerization of allylamine. Evaluation of membrane performance for the treatment of washwater and its components

Reverse osmosis membranes prepared by plasma polymerization of allylamine–nitrogen mixtures over a porous substrate were evaluated for the rejection of components present in washwater. The membranes exhibited high rejections for sodium chloride, potassium chloride, detergent, and dextrose. High rejections of urea could be achieved, but only at a sacrifice of water flux. Lactic acid could also be rejected but caused a degradation of the plasma-deposited layer.     

Preparation of composite reverse osmosis membranes by plasma polymerization. II. Copolymerization of unusual comonomers

Preparation of composite reverse osmosis membranes by plasma polymerization of 4-picoline, 3,5-lutidine, benzene, and acetylene with unusual comonomers such as H₂O and N₂ is investigated using the flow system of the monomers and an electrodeless glow discharge with 13.5 MHz radio frequency. These comonomers are incorporated into the plasma polymers and change their properties. Consequently, relatively hydrophilic polymers are formed from rather hydrophobic monomers such as benzene and acetylene by the copolymerization. The addition of H₂O and N₂ also improves the reverse osmosis characteristics of plasma polymers from hydrophilic monomers such as 4-picoline and 3,5-lutidine. The reverse osmosis characteristics of plasma polymers are influenced by the ratio of H₂O and N₂ to the basic monomer as well as by the total pressure of the monomers.     

Some experimental parameters affecting performance of composite reverse osmosis membranes produced by plasma polymerization

Reverse osmosis (RO) composite polymer membranes were prepared from the organic monomers 3-butenenitrile, propyleneimine, 4-vinylpyridine, and allylamine by plasma polymerization in a radio-frequency discharge. RO performance data (water flux and salt rejection) were obtained as a function of discharge power and deposition time. Membranes were subject to RO testing at 45°C for up to 150 hr to investigate membrane deterioration. No appreciable degradation was observed. Water flux increased significantly with time at 45°C, and improved salt rejection at 45°C was observed in most cases.     

Reverse osmosis characteristics of cellulose acetate butyrate membranes

Cellulose acetate butyrate membranes were cast from five different formulations. The pure water flux through the membrane increased with evaporation period. The separation of 4000 ppm NaCl aqueous solution remained unchanged until it reached a critical flux; at that point, separation decreased inversely proportional to the flux. Scanning electron microscope photography of the membranes corresponding to each evaporation period is reported.     

Preparation of reverse osmosis membranes by plasma polymerization of organic compounds

The plasma polymerization of organic compounds was used to prepare a composite reverse osmosis membrane which consists of an ultrathin semipermeable membrane formed by plasma polymerization of an organic compound or compounds and a porous substrate. Many nitrogen-containing compounds (aromatic amines, heteroaromatic compounds, aliphatic amines, and nitriles) were found to yield excellent reverse osmosis membranes by plasma polymerization directly onto porous substrates such as Millipore filters, porous polysulfone filters, and porous glass tubes. Factors involved in the preparation of reverse osmosis membranes by plasma polymerization were investigated and discussed. The plasma polymerized membranes have the following unique features: (1) very stable performance independent of salt concentration and applied pressure (practically no water flux decline was observed with many membranes): (2) salt rejection and water flux both increase with time in the initial stage of reverse osmosis (consequently, the performance of the membrane improves with time of operation); (3) very high salt rejection (over 99%) with high water flux (up to 38 gfd) can be obtained with 3.5% NaCl at 1500 psi (membranes perform equally well under conditions of sea water conversion and brakish water treatment).     

Novel ion-containing reverse osmosis membranes. II. Reverse osmosis properties

The reverse osmosis properties of ion-containing membranes prepared by ⁶⁰Co mutual irradiation grafting of 2-vinylpyridine to poly(3,3-bis(chloromethyl)oxetane) (polyoxetane, Penton) followed by quaternization with methyl bromide are presented. In general, the volumetric fluxes varied linearly with pressures up to 55 atm. Katchalsky's treatment of membrane permeability was used to analyze the data. Membrane constants and diffusion coefficients of water and sodium chloride were determined with membranes containing different volume fractions of water. The diffusion coefficients of water in the membranes were of the same order of magnitude as the self-diffusion coefficient of water (～3 × 10^?5 cm²/s). The diffusion coefficients of sodium chloride in the membrane were of the order of 10^?7 cm²/s. The diffusion coefficients increased with hydration, and the salt rejections were markedly affected by the external salt concentrations. The apparent energies of activation for the volumetric flux were calculated in distilled water and in 0.5% sodium chloride solution.     

Permeation of single and mixed gases through composite membranes prepared by plasma polymerization of fluorocarbon compounds

The permeations of simple permanent gases and their mixtures through plasma-polymerized composite membranes were studied. Composite membranes were prepared by the plasma polymerization of fluorocarbon monomers such as pentafluorotoluene (PFT) and pentafluoropyridine (PFP) onto porous Celgard. For pure gases, the permeability coefficients were mainly affected by diffusivity rather than solubility. The permeability coefficient decreased as the kinetic molecular diameter of the penetrant molecules increased, and the permeability coefficients were independent of pressure. For mixed gases, the permeability coefficient was not affected by the composition of penetrants for the whole range of composition.     

二次界面聚合法制备聚酰胺-脲-酰亚胺反渗透复合膜

本论文采用二次界面聚合法制备得到一种新型的聚酰胺-脲-酰亚胺反渗透复合膜。先将关键功能单体5-异氰酸酯-异酞酰氯（ICIC）与4-甲基-间苯二胺（MMPD）经单面界面聚合形成初生态的基膜,之后将关键功能单体N,N’-二甲基间苯二胺（DMMPD）与初生态基膜上残留的ICIC及未反应完的酰氯基团（-COCl）进行二次界面聚合,再经热处理、水漂洗制得一种新型的聚酰胺-脲-酰亚胺（MMPD-ICIC-DMMPD）反渗透复合膜。采用傅立叶衰减全反射红外光谱（ATR-FTIR）和X射线光电子能谱分析了膜活性分离层的化学结构,利用扫描电镜（SEM）和原子力显微镜（AFM）观察了所成膜的表面形态,同时测试了膜的耐氯性能,并以单次聚合聚酰胺-脲（MMPD-ICIC）膜作对比。结果表明：采用二次界面聚合法在功能化基膜MMPD-ICIC上引入一超薄ICIC-DMMPD层,使得所成二次聚合膜MMPD-ICIC-DMMPD的活性分离层相对稍厚,表面更光滑,且亲水性和耐氯性能更好。     

Nanofiltration membranes prepared by interfacial polymerization on thin-film nanofibrous composite scaffold

Nanofiltration (NF) membranes, consisting of a composite barrier layer prepared by interfacial polymerization of polyamide around the ultra-fine cellulose nanofibers (CN) layer in a thin-film nanofibrous composite (TFNC) scaffold, were demonstrated. Two interfacial polymerization pathways (termed IP and IP-R), regarding the arrangement of the aqueous and organic phases, were investigated. It was found that interfacial polymerization with the aqueous phase above the organic phase (IP-R) yielded better filtration performance, i.e., IP-R based membranes exhibited a higher MgCl₂ rejection than IP based membranes. Transmission electron microscopy (TEM) observation indicated that the denser part of the barrier layer was on the CN layer surface of IP-R based membranes, whereas this portion was deeply immersed in the CN layer of IP based membranes. To investigate the structure and property relationship of the composite barrier layer, both IP and IP-R based membranes were treated with 1% trimesoyl chloride (TMC) in hexane. After treatment, the rejection of NaCl was found to increase from 74% to 91% for IP-R based membranes, while remained unchanged (∼75%) for IP based membranes. This behavior can be explained by the decrease in pore size due to the cross-linking of TMC and secondary amino groups in the barrier layer of IP-R based membranes, while the permeability in IP based membranes was probably mainly controlled by the water passage through channels formed at the interface between CN and polymer matrix in the barrier layer of IP based membranes, which is not dependent of the cross-linking reaction.     

Reverse osmosis by dynamically formed cation exchanger membranes

An investigation was conducted into the behaviour of a dynamically formed membrane consisting of small particles (<5μm) of a cation exchanging ion exchanger material. Variables in the study were: NaCl concentration of the feed, pressure, rate of flow of the liquid along the membrane, and temperature. The retention values found appeared to agree quantitatively with Donnan's exclusion theory if a certain measure of leakage of the membrane was assumed. The compressibility of the membrane material explains the behaviour of product flux, leakage and capacity of the ion exchanger as a function of the pressure. The temperature has considerable influence on the permeate flux, but not on the actual retention.     

Polyacrylic desalination membranes. II. Reverse osmosis performance

A new class of polyacrylic membranes has been tested under reverse osmosis conditions on dilute (1%–4%) salt solutions. Fluxes up to 0.2 gal-mil/ft²-day at greater than 98% rejection have been achieved. The effect of membrane composition on product flux and salt rejection is discussed. Increased fluxes at even higher rejection should be possible by proper selection of the type and concentration of hydrophilic, hydrophobic, and crosslinking monomers. It is concluded that improved membranes should have as high as possible a concentration of hydrophilic groups, distributed randomly through a lightly crosslinked, rubbery polymer matrix.     

Effect of siloxane chain lengths of monomers on characteristics of pervaporation membranes prepared by plasma polymerization

Plasma-polymerized membranes were prepared from a series of monomers with the different siloxane chain lenghts, i. e., hexamethyldisiloxane, octamethyltrisiloxane, and decamethyltetrasiloxane, and effects of the starting monomers on both the structures of the plasma polymers and the pervaporation characteristics of ethanol/water mixture were investigated. By IR and XPS measurements, it was found that with increase of the siloxane chain lenghts of the monomer the siloxane chains in the plasma polymers were linked more continuously and smaller amounts of additional oxygen were newly incorporated into the polymers. All membranes obtained from the three monomers were found to be ethanol-permselective. From the standpoint of obtaining both high selectivity and high permeation rate, the monomer with the longer siloxane chain was profitable. The relations between the results of the analysis of the plasma polymers by IR and XPS measurements and the pervaporation characteristics obtained are discussed. © 1994 John Wiley & Sons, Inc.     

Pervaporation membranes for ethanol–water mixture prepared by plasma polymerization. III. Perfluorocarbon membranes

Pervaporation membranes for the ethanol–water mixture were prepared by plasma polymerization of tetrafluoroethylene, perfluoropropane, and perfluoropropylene onto porous substrates. The influence of the monomers on the elemental ratio (F/C) of the polymer depositions by X-ray photoelectron spectroscopy was rather small compared with that of the W/FM parameter (W = wattage for plasma excitation, FM = mass flow rate of a monomer). The optical emission spectroscopy indicated the similarity of gaseous species formed in the plasmas. The membranes were found ethanol-permselective, showing separation coefficients (α_EtOH) around 4–7 and a wide range of permeation rates (J), 10–10^?2 kg/m² h, for the 4.8 wt % ethanol solution at 40°C. The α_EtOH of the membranes with thicker depositions could be correlated to the F/C ratios as a measure of membrane hydrophobicity. It was thought that, by making a plot α_EtOH against J values for the perfluorocarbon membranes, they could be classified into three groups on thickness of deposition. The ethanol-separation mechanisms for each group, which may contain four kinds of mass transfer schemes, i.e., distillation through larger pores, flow of sorption layer at the liquid–membrane interface, and diffusions through deposition or substrate, were also discussed.     

Preparation of composite reverse osmosis membranes by plasma polymerization of organic compounds. IV. Influence of plasma–polymer (substrate) interaction

Preparation of composite membranes by plasma polymerization is affected not only by the type of monomer and the mode of discharge but also by the interaction of plasma–polymer substrate. Consequently, the reverse osmosis characteristics of composite membranes are dependent on the combination of substrate and monomer(s). The interactions of plasma and polymer are investigated using porous polysulfone film and cellulose nitrate–cellulose acetate (CNCA) porous film as the substrates, and acetylene/H₂O/N₂ and acetylene/H₂O/CO as the monomer systems. The effects of plasma pretreatment of the substrates on the chlorine resistance of the membranes are also investigated.     

Preparation of composite reverse osmosis membranes by plasma polymerization of organic compounds. III. Plasma polymers of acetylene/CO/H2O

Reverse osmosis characteristics of composite membranes prepared by the plasma polymerization of acetylene/CO/H₂O mixtures with various ratios of components are investigated; porous film of cellulose nitrate-cellulose acetate is used as the substrate. This monomer system seems to have the following advantages: (1) A relatively short deposition time (1–2 min) is enough to produce reasonably good reverse osmosis membranes; and (2) good chemical stability of membranes can be obtained, especially in the case of chlorine resistance.     

Surface modification of UHSPE fibers through allylamine plasma deposition. I. Infrared and ESCA study of allylamine plasma formed polymers

Allylamine (CH₂?CH? CH₂? NH₂) was polymerized through rf generated plasma at varying powers and times. Chemical groups and elemental compositions in the polymers were studied using ESCA and infrared spectroscopy. It was observed that plasma derived polymers contained a significant number of primary amines, along with some secondary and tertiary amines, imines, and nitrile groups. Plasma derived polymers had a complex structure and contained unsaturated groups. A considerable amount of oxygen, primarily from residual air in the plasma reaction chamber, and possibly from atmosphere when plasma polymers were exposed to air, was responsible for carbonyl, amide, ether, and hydroxyl groups found in the polymer structure. Some silicon was also detected in the plasma deposited films.     

界面聚合工艺条件对反渗透复合膜性能的影响

以聚砜超滤膜为支撑膜,间苯二胺(MPD)为水相功能单体,均苯三甲酰氯(TMC)为油相功能单体,通过界面聚合法制备了反渗透复合膜。研究了功能单体浓度、界面聚合反应时间、界面聚合成膜后热处理时间和温度等条件对复合膜分离性能的影响;并对在水相中添加相转移催化剂对复合膜分离性能的影响和相转移催化机理进行了初步探讨。首先在单因素实验条件下确定工艺条件的优化范围,然后经过正交实验得到最佳工艺条件,实验结果表明, 油相中TMC浓度为3 g&#8226;L^-1、水相中MPD浓度为20 g&#8226;L^-1、界面聚合反应时间为30 s、界面聚合成膜后热处理温度为90 ℃、后处理时间15 min时,所制备的反渗透复合膜表现出良好的分离性能,通量达14.91 L&#8226;m^-2&#8226;h^-1,截留率为0.951(测试条件: 压力1.6 MPa, 温度25 ℃, NaCl浓度20000 mg&#8226;L^-1);当水相中MPD浓度较低时,加入适量的相转移催化剂,能有效地改善膜的分离性能。     

Effects of polymerization conditions on the properties of poly(furfuryl alcohol) composite membranes

Poly(furfuryl alcohol) (PFA) composite membranes were prepared by polymerization of furfuryl alcohol (FA) using sulfuric acid (H₂SO₄) as the catalyst and polysulfone ultrafiltration membrane as the substrate. The membrane samples were characterized by ATR‐IR, TGA, SEM, and gas permeation technique. The effects of synthesis conditions including the FA/H₂SO₄ molar ratio, polymerization temperature, and the type of solvent on the chemical structure, surface morphology, and gas permeation properties of PFA composite membranes were studied. Our results showed that the suitable synthesis conditions for the preparation of PFA composite membranes with smooth surfaces and uniform structure include (1) FA/H₂SO₄ molar ratios: 74‐300, (2) polymerization temperatures: 80–100°C, and (3) solvents: ethanol and acetone. The PFA composite membrane prepared with a FA/H₂SO₄ molar ratio of 250, a polymerization temperature of 80°C and ethanol as the solvent exhibited the highest H₂/N₂ ideal selectivity ( $ {\rm{\alpha }}_{{\rm{H}}_{\rm{2}} {\rm{/N}}_{\rm{2}} } = 24.9 $ ), and a H₂ permeability of 206 Barrers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012